Photochromism is a known physical phenomenon that occurs in some compounds, and detailed discussion of how it works can be found in Photochromism Molecules and Systems (Studies in Organic Chemistry, Vol. 40., Edited by H. Durr and H. Bouas-Laurent, Elsevier, 1990). Pyran derivatives are conventional photochromic compounds, which have adsorption wavelength at their excitation state.
A photochromic material can be applied as a color transition lens, smart window, window film, or other photochromic applications, which need a fast and reversible photochromic characteristic. However, conventional photochromic materials have a relatively low UV adsorption coefficient (low UV sensitivity). Conventional photochromic materials also need a long time to reinstate to a transparent state. In other words, even if the conventional photochromic materials are not irradiated by UV anymore, they still cannot quickly reinstate back to transparency. In addition, conventional photochromic materials have a high melting point and poor solubility, making them difficult to process and requiring the addition of other materials (e.g. liquid-crystal, solvent, or polymer) for improving their processability. Accordingly, a novel photochromic material for overcoming the above shortcomings is called for.